Re: [PATCH v3 07/33] drm/vkms: Introduce configfs for plane name

Luca Ceresoli
2025-12-23T11:14:13Z

On Mon Dec 22, 2025 at 11:11 AM CET, Louis Chauvet wrote:
> Planes can have name, create a plane attribute to configure it. Currently
> plane name is mainly used in logs.
>
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> ---
> Documentation/ABI/testing/configfs-vkms | 6 +++++
> Documentation/gpu/vkms.rst | 3 ++-
> drivers/gpu/drm/vkms/vkms_configfs.c | 43 +++++++++++++++++++++++++++++++++
> 3 files changed, 51 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/ABI/testing/configfs-vkms b/Documentation/ABI/testing/configfs-vkms
> index 0beaa25f30ba..6fe375d1636f 100644
> --- a/Documentation/ABI/testing/configfs-vkms
> +++ b/Documentation/ABI/testing/configfs-vkms
> @@ -103,6 +103,12 @@ Description:
> Plane type. Possible values: 0 - overlay, 1 - primary,
> 2 - cursor.
>
> +What: /sys/kernel/config/vkms/<device>/planes/<plane>/name
> +Date: Nov 2025
> +Contact: dri-devel@lists.freedesktop.org
> +Description:
> + Name of the plane.
> +
> What: /sys/kernel/config/vkms/<device>/planes/<plane>/possible_crtcs
> Date: Nov 2025
> Contact: dri-devel@lists.freedesktop.org
> diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> index 1e79e62a6bc4..79f1185d8645 100644
> --- a/Documentation/gpu/vkms.rst
> +++ b/Documentation/gpu/vkms.rst
> @@ -87,10 +87,11 @@ Start by creating one or more planes::
>
> sudo mkdir /config/vkms/my-vkms/planes/plane0
>
> -Planes have 1 configurable attribute:
> +Planes have 2 configurable attributes:
>
> - type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
> exposed by the "type" property of a plane)
> +- name: Name of the plane. Allowed characters are [A-Za-z1-9_-]
>
> Continue by creating one or more CRTCs::
>
> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
> index 506666e21c91..989788042191 100644
> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
> @@ -324,10 +324,53 @@ static ssize_t plane_type_store(struct config_item *item, const char *page,
> return (ssize_t)count;
> }
>
> +static ssize_t plane_name_show(struct config_item *item, char *page)
> +{
> + struct vkms_configfs_plane *plane;
> + const char *name;
> +
> + plane = plane_item_to_vkms_configfs_plane(item);
> +
> + scoped_guard(mutex, &plane->dev->lock)
> + name = vkms_config_plane_get_name(plane->config);

vkms_config_plane_get_name() returns a pointer to the name string, not a
copy. Unless I'm missing something, that string might be freed before the
next lines, where it is used:

> +
> + if (name)
> + return sprintf(page, "%s\n", name);
> + return sprintf(page, "\n");

So for safety the above 3 lines whould go inside the scoped_guard().

> +}
> +
> +static ssize_t plane_name_store(struct config_item *item, const char *page,
> + size_t count)
> +{
> + struct vkms_configfs_plane *plane;
> + size_t str_len;
> +
> + plane = plane_item_to_vkms_configfs_plane(item);
> +
> + // strspn is not lenght-protected, ensure that page is a null-terminated string.
> + str_len = strnlen(page, count);
> + if (str_len >= count)
> + return -EINVAL;
> +
> + if (strspn(page, "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_-") != count - 1)
> + return -EINVAL;

I see you effor to make this as clean as possible, thanks. Still this is a
tad ugly, and should be moved to some common place at some point IMO. For
now it's fine, but if you need to add more user-passed strings, that could
be the moment to move this code.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering